Pressure sensor semiconductor dies include a diaphragm for sensing pressure. The sensed pressure is converted to an electrical parameter such as change in resistivity. Pressure sensor dies are typically encased in a molding compound to protect the connections to the die and the die itself from corrosion and other adverse effects. Molding compounds typically have an elastic modulus of greater than 1 GPa at room temperature and therefore are relatively hard. Conventional molded pressure sensor packages have a window in the molding compound over the diaphragm of the pressure sensor die so that the diaphragm is not covered by the molding compound.
Thermo-mechanical expansion of the molding compound imparts significant stress on the molded die, causing tension on the diaphragm even though the diaphragm is not covered by molding compound. The stress caused by the thermo-mechanical expansion of the molding compound can cause unacceptable variations in the pressure behavior of the sensor depending on the robustness of the membrane of the diaphragm. Some conventional pressure sensor packages include a glob top covering both the lateral side and top side of the die with the diaphragm in order to reduce this stress, by providing a softer buffer between the chip and the molding compound. However in this approach the glob top contacts the die terminals and part of the electrical connections between the die terminals and leads of the package. Glob top is a less effective barrier than molding compounds at blocking harmful chemicals such as H2SO4, etc., resulting in less component protection and early failure.